What Is Henoch-Schönlein Purpura Nephritis and How Does It Affect the Kidneys?

Henoch-Schönlein purpura nephritis (HSPN), often referred to simply as "purpura kidney," is a form of secondary glomerular disease triggered by Henoch-Schönlein purpura (HSP)—a systemic vasculitis primarily affecting small blood vessels. This condition arises when immune complexes, particularly those containing immunoglobulin A (IgA), deposit in the glomeruli, capillaries, and basement membranes of the kidneys. These deposits incite inflammation, increasing vascular permeability and weakening vessel walls, which ultimately compromises kidney function.

Understanding the Underlying Mechanism

The root cause of HSPN lies in abnormal immune responses. Elevated levels of IgA-containing immune complexes circulate in the bloodstream and become trapped in the delicate filtering units of the kidneys. This triggers an inflammatory cascade that damages the glomerular structure. Over time, this damage can impair the kidney's ability to filter waste and retain essential proteins, leading to clinical signs such as proteinuria and hematuria.

Common Symptoms and Clinical Presentation

Patients with HSP typically present with a classic tetrad of symptoms: palpable skin purpura (most commonly on the lower extremities), joint pain (arthralgia), abdominal discomfort, and renal involvement. When the kidneys are affected, abnormalities appear in urinalysis—most notably protein in the urine (proteinuria) and occult blood (hematuria). In more advanced cases, red blood cells become visible to the naked eye, resulting in gross hematuria.

Timing of Renal Involvement: A Critical Window

One of the most important clinical insights is that kidney involvement usually occurs 4 to 6 weeks after the initial onset of skin purpura. This delayed manifestation means that even if a patient appears to be recovering from the early phases of HSP, ongoing monitoring is essential. Parents and caregivers should be advised not to dismiss the rash as a minor issue but to follow up with urine tests during this critical period to catch any developing renal complications early.

Diagnosis and Monitoring

Early detection through routine urinalysis can significantly influence long-term outcomes. Persistent proteinuria or microscopic hematuria warrants further evaluation, potentially including blood tests for kidney function (such as serum creatinine and eGFR) and, in some cases, a kidney biopsy to assess the extent of glomerular damage. Pediatric patients are especially vulnerable, making vigilant follow-up crucial in children diagnosed with HSP.

Why Awareness Matters

Despite being classified as a rare disease, HSPN is one of the most common forms of vasculitis-induced kidney injury in children. Raising awareness among parents, educators, and primary care providers can lead to earlier diagnosis and better management. Prompt intervention may prevent progression to chronic kidney disease or, in severe instances, end-stage renal failure.

In summary, Henoch-Schönlein purpura nephritis is a serious but manageable complication of a seemingly mild autoimmune disorder. Understanding its pathophysiology, recognizing the timing of renal involvement, and implementing timely screening are key steps in protecting kidney health and ensuring favorable patient outcomes.